Citrus growers describe living with tree disease

In 2005, Florida citrus production was humming along, and growers were sending the vast majority of the nation's juice oranges and grapefruit to market. The Asian citrus psyllid had been present in groves since 1998, but growers looked at it as an insect of no economic importance.

Then, citrus trees started to die, after first beginning to produce oddly colored, green, misshapen fruit and losing foliage. Florida growers knew then the citrus greening disease known as huanglongbing had invaded, and the psyllids were spreading it statewide.

Citrus growers from Florida and Texas—who are living with the consequences of an uncontrolled, invasive pest—recounted their experiences to nearly 700 growers and packers attending the annual California Citrus Mutual Citrus Expo in Visalia.

Larry Black, general manager of Peace River Packing in Lakeland, Fla., said growers there now struggle with much lower yields plus fruit lacking in solids, size and flavor.

"I was handling a million boxes a year. Now we are at half that. It is devastating for growers and they can't do enough—even spraying 12 times a year," Black said.

Dale Murden, president of Texas Citrus Mutual, told growers his state is now in the fifth year after the first positive HLB find. The latency of the disease is hard to understand, he said, but Texas growers are learning from their counterparts in Florida.

"Don't let your guard down with ACP," Murden warned growers, referring to the psyllid. "Texas at five to six years after that first find is at a scary crossroad."

In order to keep citrus production viable, Murden said Texas asks growers to communicate about psyllid control in citrus, form management areas and adopt zero tolerance for psyllid populations. They have been able to achieve about 90 percent compliance with their control protocols, he said.

"Make ACP your No. 1 target," he advised.

In Florida and Texas—and now California—abandoned or unfarmed citrus groves pose a problem for psyllid control. Murden said in areas of larger citrus plantings in Texas, removal of infected trees has been aggressive.

Black said one problem in Florida is that not all growers are on board with an aggressive treatment program to suppress the psyllid. Large growers in the southern part of the state work together and do aerial sprays, but those with smaller acreages are not as vigilant.

Urban detection and removal of infected trees is another tough situation in Florida. Ric Freeman, who farms citrus in Winter Garden, said an earlier citrus canker outbreak led to removal of infected trees and when the HLB infections began to spread, there was "no appetite" on the state level for enforcement.

Freeman told California growers he believed they could stall HLB spread to citrus-growing areas for another 10 years with aggressive spray programs.

"Do the right job, work with your neighbors," he advised.

Citrus growers and the U.S. Department of Agriculture have funded millions of dollars of research into the bacterial disease and the psyllid. At the Visalia event, researchers spoke to growers about their current projects, what they hope to accomplish and what growers can to do suppress the psyllid in California.

The pest has been trapped in most citrus-growing areas of the state, but no HLB-infected trees have been found outside of urban Southern California; a 12th infected tree was recently identified in La Puente.

Infected trees are sources of the pathogen that can be spread to other citrus trees by psyllids feeding on new growth; see related story. Infected trees may not show symptoms for two years. It is believed that early detection of HLB and removal of infected trees can slow progression of the disease throughout an orchard.

Wenbo Ma, a plant pathologist at the University of California, Riverside, was awarded a $4 million, five-year USDA grant to pursue work on early detection of HLB in citrus. She is working on development of antibody-based HLB detection methods to find the disease in its early stages.

Currently, there is little understanding of systemic analysis, Ma said. Another challenge is the inability to grow the bacteria in a laboratory. She said one goal of her research is to learn how the bacteria affect different varieties of citrus.

USDA research horticulturist Ed Stover said he is optimistic about future citrus production in Florida, in spite of the massive losses due to HLB.

Estimating that nearly 90 percent of commercially grown Florida citrus trees are infected, Stover said there is no evidence that infected trees can be cured with existing technologies. Research investment by the federal government plus grower-funded research will generate options for future plantings with HLB-resistant or -tolerant trees, he said. "Replacement" citrus varieties or transgenics may be essential to the HLB solution, Stover added.

He pointed out that nearly all sweet orange varieties come from a hybrid citrus that originated in China more than 1,000 years ago. Since 2010, he said, researchers in Florida have been scouting multiple-variety citrus groves, looking for trees that appear to be resistant or tolerant to HLB infection.

Stover said the Florida citrus-breeding program is looking at a broad selection of parent material, and the 2,000 new hybrids produced each year are from crosses intended to achieve HLB tolerance or resistance. A viable alternative to crossbreeding for resistance/tolerance, Stover said, is transgenics.

"This appears to be the most promising solution for strong HLB resistance or perhaps immunity," he said, noting work done at Texas A&M with transgenic red grapefruit and sweet orange.